The present invention is directed to a lithium-air battery having high capacity and recycle efficiency.
Lithium ion technology has dominated the market as an energy source for small electronic devices and even hybrid electric vehicles. However, Li-ion batteries have insufficient theoretical capacity to be a power source for future high capacity generations of power sources capable to run an electric vehicle.
Metal-air batteries have been under investigation as advanced generation of high capacity energy sources that have the potential to power vehicular devices for distances comparable to present hydrocarbon based combustion engines. In a metal-air battery, the metal of the anode is oxidized and the resulting cation travels to the cathode zone containing a porous matrix of a material such as carbon, for example, where oxygen is reduced and the reduction product as oxide or peroxide combines with the metal cation to form the discharge product. Upon charge, this process is ideally reversed. Metal-air batteries are recognized to have potential advantageous properties over metal ion batteries because the cathodic material, oxygen, may be obtained from the environmental air atmosphere and thus the capacity of the battery would in theory be limited by the anodic metal supply. Thus, oxygen gas would be supplied continuously from outside the battery and battery capacity and voltage would be dependent upon the oxygen reducing properties and chemical nature of the discharge product formed.
Lithium air batteries have the potential to supply 5-10 times greater energy density than conventional lithium ion batteries and have attracted much interest and development attention as a post lithium ion battery technology. For example, a nonaqueous lithium air battery which forms Li2O2 as discharge product theoretically would provide 3038 Wh/kg in comparison to 600 Wh/kg for a lithium ion battery having a cathodic product of Li0.5CoO2. However, in practice, the metal air technology and specifically current nonaqueous lithium air batteries suffer many technical problems which have prevented achievement of the theoretical capacity.
The capacity of the Li air battery is highly dependent upon the capacity of the cathode matrix to store the Li2O2 discharge product. Li2O2 is generally insoluble in conventional nonaqueous solvents employed in metal air batteries. Therefore, upon formation at the cathode matrix the Li2O2 precipitates and fills the surface porosity of the matrix thus preventing access to the vacant capacity of the matrix interior region. Moreover, Li2O2 is an insulator and therefore, once the surface of the matrix is coated, oxygen reduction is prevented and discharge terminated, i.e., the capacity of the battery is severely reduced in comparison to the theoretical capacity.
As indicated above, effort to produce an efficient high capacity lithium air battery has received much attention.
Gordon et al. (WO 2008/133642) describe a metal (Li, Na, K) air battery having a metal anode, an ion selective membrane separating the anode from the cathode and forming distinct compartments for each electrode. The catholyte is aqueous and the metal hydroxide or metal peroxide formed at the cathode is retained as a solute in the aqueous catholyte.
Hartmann et al. (Nature Materials, Vol. 12, March, 2013, 228-232) describe construction of an electrochemical cell having a sodium anode and glass fiber air cathode. The electrolyte was diethylene glycol dimethyl ether with sodium triflate as solute. The cell was compared to a similarly constructed lithium electrochemical cell and the authors concluded that a sodium air battery may have properties which are advantageous over a lithium air battery.
Peled et al. (WO 2011/154869) describe a metal air battery wherein the metal anode is employed in a molten state. The molten anode is separated from the catholyte by a Solid Electrolyte Interphase (SEI) film. Multiple metals including sodium, lithium, potassium, rubidium, cesium and alloys thereof are described and sodium appears to be the preferred embodiment.
Lu et al. (U.S. 2014/0075745) describe a alkali/oxidant battery having an anode of an alkali metal including lithium, sodium and potassium, a separator of an ion permeable membrane and a cathode of NiOOH, Mn+4O2 or Fe+3(OH)3. The anolyte ion is the cation of the anode metal and the catholyte contains both the cathode active material and the alkali metal hydroxide.
Barde et al. (U.S. 2013/0316253) describes a method to prepare an oxygen cathode by forming a catalytic material on a surface of a carbonaceous substrate. α-MnO2 is an example of the catalytic material formed on the carbon. A lithium air cell containing the cathode material is described. The cell does not contain an ion specific permeable membrane and the electrolyte active ion is Li+ throughout the cell.
Visco et al. (U.S. 2013/0045428) describes an aqueous lithium air battery wherein the lithium anode is protected from the aqueous catholyte by a lithium ion conductive membrane. Lithium salts are present in the catholyte along with an organic acid having acidity of sufficient strength to dissolve lithium carbonate.
Chase et al. (U.S. 2012/0028137) describe a metal air electrochemical cell wherein the electrolyte contains an “oxygen evolving catalyst” (OEC). Convention cell structure is employed and the OEC on charging catalyzes the oxidation of metal oxides in the air electrode and electrolyte.
Visco et al. (U.S. Pat. No. 8,455,131) describe a lithium air cell having a lithium anode protected by a lithium ion conductive membrane in communication with an aqueous catholyte air cathode. The catholyte contains a halide salt in addition to a lithium salt such that the humidity of the cathode compartment is controlled. A sodium halide is not disclosed as a halide salt and an anode compartment containing a lithium anolyte separated from the cathode compartment by a lithium ion conducting membrane is not disclosed.
Visco et al. (U.S. Pat. No. 7,491,458) describe a lithium fuel cell wherein the anode is protected from the electrolyte by a lithium ion conductive membrane. This reference does not disclose or suggest a lithium air battery having a structure according to the present invention.
In spite of the significant ongoing effort there remains a need to develop and produce an efficient, safe, cost effective, high capacity lithium air battery useful especially for powering vehicles to distances at least equal to or competitive with current hydrocarbon fuel systems.